Fix CLASS_LOADER_TYPE_CACHE OOM issue with WeakHashMap

[kylixs]

Problem

The CLASS_LOADER_TYPE_CACHE in SWDescriptionStrategy uses a two-level cache structure with ClassLoader.hashCode() as the first-level key and type
name as the second-level key. In scenarios involving rule engines like Drools that dynamically generate large numbers of classes, this cache grows
indefinitely and causes OutOfMemoryError during long-running applications.

Original Discussion, apache/skywalking#12627

Root Cause

1. No cache cleanup mechanism: The cache retains entries permanently, even after ClassLoaders are garbage collected
2. HashCode collision risk: Different ClassLoaders may have the same hashCode, causing cache conflicts
3. Memory leak: Dynamic classes are typically used once but their cache entries persist forever

Solution

Replace the hashCode-based cache with a WeakHashMap that automatically cleans up entries when ClassLoaders are garbage collected:

  // Before: Memory leak prone
  private static final Map<Integer, Map<String, TypeCache>> CLASS_LOADER_TYPE_CACHE = new ConcurrentHashMap<>();

  // After: Automatic cleanup
  private static final Map<ClassLoader, Map<String, TypeCache>> CLASS_LOADER_TYPE_CACHE =
      Collections.synchronizedMap(new WeakHashMap<>());

Key Changes

1. WeakHashMap Implementation: Automatically removes cache entries when ClassLoader is GC'd
2. Direct ClassLoader Reference: Use ClassLoader object as key instead of hashCode to avoid collisions
3. Bootstrap ClassLoader Handling: Separate cache for null ClassLoader since WeakHashMap doesn't support null keys

• If this pull request closes/resolves/fixes an existing issue, replace the issue number. Closes #.
• Update the CHANGES log.

[Copilot]

Pull Request Overview

This PR fixes an OutOfMemoryError issue in the SWDescriptionStrategy cache by replacing a hashCode-based cache with WeakHashMap for automatic cleanup when ClassLoaders are garbage collected. This addresses memory leaks in scenarios involving dynamic class generation like Drools rule engines.

• Replaces HashMap with WeakHashMap to automatically clean up cache entries when ClassLoaders are GC'd
• Adds separate handling for bootstrap ClassLoader since WeakHashMap doesn't support null keys
• Includes comprehensive test coverage for the new cache behavior

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
SWDescriptionStrategy.java	Implements WeakHashMap-based cache and bootstrap ClassLoader handling
SWDescriptionStrategyCacheTest.java	Adds test coverage for WeakHashMap cleanup, bootstrap handling, and concurrent access

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[wu-sheng]

@gaojingyuan001 @hyhyf This one.

[wu-sheng]

@gaojingyuan001 @hyhyf Any of you tried this one? This PR was raised due to your use cases.

[wu-sheng]

@kylixs As this is an enhancement and it seems no harm to the whole system, could you update the changes and we consider to merge this if there is no further feedback?

[Ax1an]

After applying this update for a week, the service using Drools no longer experienced memory leaks. I think it can be merged. @wu-sheng @kylixs

[wu-sheng]

After applying this update for a week, the service using Drools no longer experienced memory leaks. I think it can be merged. @wu-sheng @kylixs

Thanks for the feedback.

@kylixs waiting for you to update change logs.

[kylixs]

After applying this update for a week, the service using Drools no longer experienced memory leaks. I think it can be merged. @wu-sheng @kylixs

Thanks for the feedback.

@kylixs waiting for you to update change logs.

done